Coated wrapping tissue and process of making same



Patented Apr. 17, 1951 COATED WRAPPING TISSUE AND PROCESS OF MAKING SAME Arthur Douglas McLaren, Brooklyn, N. Y., as-

signor to E. I. du Pont deNemours & Company, Wilmington, DeL, a corporation 'of Delaware No Drawing. Application February 13, 1948, Serial No. 8,299

11 Claims. 1

This invention relates to processes for effecting physical bonding between materials and to articles so bonded, and is more particularly directed to processes for bonding materials having negatively charged surfaces to water-insoluble, heat-softenable, organic polymers containing recurring dipole groups. Still more particularly, the invention relates to the productionof transparent regenerated cellulose film provided with a well-adhered moisture proofing coating of vinylidene chloride copolymer.

This application is a continuation-in-part of my prior application Serial No. 648,833, filed February 19, 1946, now abandoned, as Wrapping Tissue and Process.

The desirability of effecting improved bonding between materials has been recognized in a variety of situations. It has been realized that composite structures made up of dissimilar materials could possess the advantageous properties of each of the constituent materials and at the same time have additional, especially desirable properties resulting from the combination, if only suitable Ways of effecting permanent joining of the materials could be found.

The problems of adhesion are particularly troublesome when at least one of the materials to be joined has a negatively charged surface, such as is present for instance in regenerated cellulose sheet and like materialscontaining a substantial proportion of negative groups such as hydroxyl groups on their surfaces. Bonds to such negatively charged materials tend to be easily disrupted by moisture.

To mention a particular instance, an outstanding problem in the utilization of vinylidene chloride copolymers as coatings for smooth, dense, non-fibrous, hydrophilic, hydroxylated organic polymer structures such as regenerated cellulose film, to be used as transparent wrapping tissue, etc., has been to adhere the coating to the base sheet. Vinylidene chloride copolymers such as vinylidene ch1oride-acrylonltrile copolymer and vinylidene chloride-vinyl chloride copolymer adhere very poorly to regenerated cellulose film and the like and the usual expedients for anchoring conventional moistureproofing coating to base film do not in general yield satisfactory results when applied to the copolymers. adhesion is obtained, full advantage cannot be taken of the desirable properties of moistureproofness, heat-scalability, flexibility, toughness, etc, inherent in such polymers.

vinylidene chloride copolymer coatings are Obviously, unless a high order of representative of a class of polymers which may be designated as water-insoluble, heat-soften able organic polymers containing recurring di pole groups, and regenerated cellulose film is representative of the class of materials which may be designated as having negatively charged surfaces.

It is an object of this invention to provide improved methods for bonding such organic polymers to negatively charged surfaces and to provide the improved bonded structures so pro-' duced. A more specific object is to tightly bond vinylidene chloride copolymer coatings to regenerated cellulose and similar base film. Another object is to treat regenerated cellulose film whereby to promote adhesion of the film to vinylidene chloride copolymers. A further object is to provide a flexible, transparent, moisture-proof sheet wrapping tissue comprised of regenerated cellulose having a strongly anchored coating of vinylidene chloride copolymer. These and other objects will more clearly appear hereinafter. H

The foregoing and other objects are accomplished according to this invention by processes in which contact is effected between a negatively charged surface and the metal atom of 2. Werner type complex compound in which a trivalent nuclear atom of a metal of the group consisting of chromium, manganese, iron, cobalt, and nickel is coordinated with the carboxylic acido group from the class consisting of aliphatic carboxylic acido groups having less than 6 carbon atoms in the chain and bearing at least one dipole group and aromatic carboxylic acido groups bearing at least one dipole group and a coating of a water-insoluble, heat-softenable, organic poly' mer containing recurring dipole groups is ap-'- plied thereto, and are further accomplished by the bonded structures so produced. More specific objects of the invention are accomplished by processes which comprise treating, e. g., by im-'- pregnating, a smooth, dense, flexible, non-fibrous sheet or film of a hydrophilic hydroxylated organic polymer such as regenerated cellulose with a solution of a compound of the Werner type in' which a trivalent nuclear atom of a metal of the group consisting of chromium, manganese, iron; cobalt and nickel is coordinated with a carboxylic acido group from the class consisting of aliphatic carboxylic acido groups having less than six' carbon atoms in the chain and bearing dipole groups and aromatic carboxylic acido groups bearing dipole groups, drying the treated film to remove solvent and thereafter coating the,

. 3 I dried film with a vinylidene chloride copolymer in the usual fashion,

In the bonded structures of my invention the Werner-type compound serves as an anchoring agent to hold the organic polymer to the negatively charged surface. The metal atom of the Werner complex coordinates with the strongly negative groups such as hydroxyl groups on the negatively charged surface and the dipole groups of the Werner compound are anchored to the organic polymer by dipole attraction.- Accordingly the bond between the dipole groups must be regarded as a physical bond since there is no chemical interaction between these groups. p

In a specific embodiment of the invention the negatively charged material may be in the form of a base sheet or film which is smooth, dense, flexible, and non-fibrous and consists of any hydroxylated organic material which is hydrophilic,-that is, absorbs or adsorbs water, for example, regenerated cellulose, lowly substitute'd cellulose esters (cellulose acetate, cellulose propionate, cellulose nitrate, etc.) lowly substituted cellulose ethers (ethyl cellulose, methyl cellulose, etc), polyvinyl alcohols, polyvinyl butyraL'hydrolyzed vinyl acetate interp-olymers, and the like. 7 However, because of its commercial availability, cheapness, generally desirable properties and present importance, regenerated cellulose is a preferred base material and the invention will be further described with specific reference thereto.

The compounds of the Werner type (hereinafter termed anchoring agent) useful for purposes of my invention are the soluble complex compounds produced byprocesses in which contact, in' the substantial absence of water, is effected between carboxylic acids of the group consisting of aliphatic carboxylic acids having less than six carbon atoms in the chain and bearing at least one'dipole substituent and aromatic carboxylic acids bearing at leastone dipole substituent, and basic salts of trivalent chromium, manganese, iron, cobalt or nickel with a mono-basic acid, the basicity of the metal salts being no greater than about 50%. The general methods disclosed in Iler, U. S. Patents Nos. 2,273,040 and 2,356,161, are suitable for the preparation of the complexes us ful herein. Chromium complexes are specifically preferred for purposes "of this invention. Examples of carboxylic acids used in the production of these complexes include mono-, di, and tri-chloro acetic acids and other chloro-. bror oor iodoaliphatic acids of a chain length of less than six carbon atoms, nitroacetic acid, hydroxyacetic acid, cyanoacetic acid; acids bearing oxygen or nitrogen heterocyclic radicals such as indolacetic acid; amino acids including polyp ptides: nitrobenzoic acid, hydroxybenzoic acid, cyanobenzoic acid, 3,5-dinitrosalicylic acid, phenoxyacetic acid, etc.; in short, any carboxylic acid (of. short chain length if aliphatic) bearing dipole groups having moments [the moment, e. g., in chloroacetic acid is that of (3-01 (1.9 D. U.)] within the range of from 0.1 to Debye units.

The organic polymer which is bonded to the anchoring agent by dipole forces should be substantially Water insoluble. That is, 10,000 parts of water should not dissolve more than about 1 part by weight of the polymer.

The organic polymer should also be heatsoftenable. There are included within this class the types of polymers known as thermoplastic and also thermosetting resins prior to curing.

Thermoplastics, of course, are those organic polymers which remain soft permanently under heat.

The organic polymer should also contain recurring dipole groups. By dipole groups is meant groups which exhibit a substantial dipole moment. The groups C-Cl, C-CN, C-OH, C-COOI-I, CNH2 are, for example, such dipole groups. The C-Cl group occurs recurrently in vinylidene chloride polymers, for instance; the C--CN group appears recurrently in acrylonitrile, the C-OH group appears recurrently in cellulose polymers, and other dipole groups which may be used according to this invention appear recurrently-in a similar manner in other polymers.

Representative, therefore, of water-insoluble, heat-softenable organic polymers containing recurring groups which may be bonded by dipole forces to the anchoring agent according to this invention are'condensation polymers such as phenol-formaldehyde and urea-formaldehyde resins in the uncured state, nylons, glycerol-unsaturated acid condensation products and high molecular weight ethylene oxide condensation pro-ducts; vinyl polymers such as polystyrene, polyvinyl chloride, neoprene, polyvinyl acetate,

polymethacrylate polymers, vinylidene chloride polymers and polymers based on phthalic anhydride reacted with unsaturated alcohols; and cellulose plastics such as regenerated cellulose and cellulose acetate. I

Treatment of the material having negatively charged surface with the Werner complex may be accomplished in any suitable fashion which insures intimate contact of the complex with the film. In treating regenerate-d cellulose film, for instance, the most convenient and economical procedure is to incorporate the anchoring agent in the aqueous softening bath. through which the gel regenerated film is ordinarily brought in the course of manufacture. The amount of chromium or other Werner complex incorporated in or on the film may vary from 0.2 to over 1% by weight (calculated as CrzOs in the case of chromium) based on the weight of the dry sheet. Preferably the anchoring agent should be applied in amounts within the range of 0.5% to 1.0%.

Compounds of the Werner type formed from basic trivalent.metal chlorides when employed in'accordance with this invention should be neutralized simultaneously with or subsequent to :Per cent Urea 16.5 Sodium formate 5.0 Formic acid 0.2

Water l 78.3

has been found particularly effective.

Because of their superior moistureproofness and heat seal characteristics copolymers of vinylidene chloride with acrylonitrile and particularly methyl ethyl ketone-soluble copolymers of vinylidene chloride with acrylonitrile wherein the weight ratio of vinylidene chloride to acrylonitrile is from 4:1 to 19:1, constitute the preferred vinylidene chloride copolymers to be joined by dipole forces to the particular negatively charged surface, regenerated cellulose film, according to this invention. However, for such film any other organic solvent soluble, film-forming vinylidene chloride copolymer may be similarly employed in accordance with the principles of this invention. Such polymers include, by way of example, the copolymers of vinylidene chloride with vinyl chloride, with vinyl acetate, with divinyl ether, with styrene, with acryl acrylates or with alkyl esters of substituted acrylic acids. The preparation of vinylidene chloride-acrylonitrile copolymers containing at least 80% vinylidene chloride and soluble in or anic solvents, e. g., methyl ethyl ketone, is described and claimed in United States patent application of Chester R. Hardt, Serial No. 605,185 filed July 14, 1945.

The application of the organic polymer to be bonded by dipole forces may be accomplished in any suitable manner such as by passing the negatively charged surface material containing the anchoring agent thereon through an organic solvent-solution of the polymer, by spraying or brushing such a solution on the treated base, or'

by superimposing the polymer upon the treated base and heating. When the polymer is to be applied by solution as a coating, any excess of coating may be removed by the usual expedients inculding doctor blades. doctor rolls, etc.

When the organic polymer is to be applied as a solution to a base film'such as regenerated cellulose, for optimum results a solution containing about solids, such as vinylidene chloride copolymer with acrylonitrile, is applied in an amount suflicient to uuiformlv deposit about 8 grams per square meter of copolymer on the base film. However. depending on the equipment and method of coating used, and degree of moistureproofness desired solutions containing more or less solids, and coatin s of greater or lesser thickness can be applied with good result.

It will be understood that, whatever the method of applying the polymer, the conditions of application are not such as to effect chemical reaction between the anchoring agent and the polymer but that the bonding which occurs between the polymer and anchorin agent is effected by dipole forces and is a physical bond.

With special reference to the coating of re enerated ce lulose film with or anic polymer through an anchoring agent, the term anchor or equivalent expressions is used herein to, mean the securing of the surface or top coatin on the base to t e. end that the coating will not loosen. slough. blister, or flake from the base film even when the coated film is sub ected to a wide range of temperature and hum dity conditions (up to 100%R. H.), etc. Moistureproofness, heat seal bond strength. and kindred terms and expressions are defined in U. S. Patent No. 2,147.180

'(Ubben) and are employed herein in accordance with such definitions.

The following examples. wherein are set forth preferred embodiments. will further illustrate the principles and practice of this invention. Throughout the specification and claims, parts and percentages are by weight unless otherwis indicated.

Example I 450 gauge regenerated cellulose gel film was run through an aqueous glycerol softening bath consisting of:

Parts An isopropyl alcohol solution containing 30% benzyloxyacetochromic chloride 20 Glycerol 60 Water 600 Neutralizing agent 24 The neutralizing agent consisted of:

Percent Urea 16.5 Sodium formate 5.0 Formic acid 0.2

Water 78.3

A 450 gauge regenerated cellulose gel film was impregnated as in Example I with a composition consisting of Parts An isopropanol solution containing 30% of a chromium complex of cyanoacetic acid 20 Glycerol 60 Water 600 Neutralizing agent (same as in Example 1) 24 and the dried film containing 0.73% chromium calculated as CrzO: was coated with vinylidene chloride-acrylonitrile copolymer as in Example I. The heat seal strength of the resulting coated film was about 400 grams as compared with 67 grams for the control.

Example III 450 gauge regenerated cellulose gel film was impregnated with a composition consisting of:

Parts A 30% isopro anol solution of chromium comp ex of 3,4-dinitrosalicylic acid 23 Glycerol 60 Water 600 Neutralizing agent (same as in Example 1) '27 and thereafter dried. The dried film was coated on both sides with the coating composition of Example I and the solvent removed to yield a coating having a total thickness of 0.28 mil.

The heat seal strength of the coated film so produced was 126 grams which compares with 40 grams for the control, and 6 grams for a substantially identical film wherein the dipole-containing anchoring agent was replaced with stearato chromic chloride.

An outstanding advantage of my invent-ion as shown in the foregoing examp es is that it enables the art to take full advantage of the'imanifestly desirable characteristics of vinylidene chloride copolvmers as protective coatings for a wide variety of dense, smooth, non-fibrous structures of hydrophilic hydroxylated organic polymers, particularly regenerated cellu ose, polyvinyl alcohoL' etc, and thus widens the field of utility and enhances the effectiveness of v said polymers and copolymers.

Example IV A 450gauge regenerated cellulose film was im- .pregnated as in Example I with a composition consisting of an isopropanol solution containing 30% of a chromium complex of trichloracetic acid, together with glycerol, water, and neutralizing agent in the proportions of Example I and the dried film was coated with a copolymer containing 60 parts of vinylidene chloride and 40 parts of vinyl chloride dissolved in a solvent containing equal parts by weight of toluene and methyl isobutyl ketone.

' The heat seal strength of the resulting coated film was about 132 grams'as compared with 40 grams for the control.

Examplell V A coated regenerated cellulose film was pre- "pared exactly as in Example IV except that the Example VI A coated regenerated cellulose film was prepared exactly as in Examples IV and V except 7 that the anchoring agent was a Werner complex .of 2-nitro-2-methylpropionic acid with chromium.

The heat seal strength of the resulting coated film was about 114 grams as compared with 40 grams for the control. 7 v

The'dipolemoment of the trichloracetic acid radical in Example IV wasabout 1.0 Debye units,

the. dipole moment of the dinitrosalicylic radical in Example V was about 3.9 Debye units, and the dipole momentoi the 2-nitro-2-niethylpropionic .acid radical in Example VI was 3.1 Debyeunits.

. As many widely different embodiments can obviously be made without departing'from the spirit and scope of my invention, it is to be understood that it is not to be restricted in any way save as set forth in the appended claims.

I claim:

. 1. ,A wrapping tissue comprising a dense, smooth, non-fibrous base sheet of hydrophilic, hydroxylated organic polymer, a coating on said base sheet comprising essentially a vinylidene chloride copolymer and an intermediate anchoring medium comprising essentially a compound of theWerner type in which a trivalent nuclear atom ofametal of the group consisting of chromium, manganese, cobalt, and nickel is coordinatedwith a carboxylic acido group from the "class consisting of saturated aliphatic. carbo-xyli'c acido-groups havinglessthan six carbonatoms in the chain and bearing at least-one dipole group and aromatic carbox-ylic acido groups bearing at leastonedipole group, the amount of said anchoring medium being from 0.2% to 1.0% by weight, calculated as the oxide'of the trivalent i netaLbased on'the dry weight of the base sheet.

"and nickel'is coordinatedwith a.carboxylic acido groupfrom' the class consisting of saturated all;- pha-tic carboxylic, acido groups having less than six carbon atoms in the chain and bearing at least one dipole group and aromatic carboxylic acido groups bearing at least one dipole group, the dipole group moments of said dipole groups being Within the range of from 0.1 to 15 Debye units, the amount of said anchoring medium being from 0.2% to 1.0% by weight, calculated as the oxide of the trivalent metal, based on the dry weight of the base sheet.

3. A wrapping tissue comprising a dense, smooth, non-fibrous transparent base sheet of hydrophilic, hydroxylated organic polymer, a

coating on said base-sheet. comprising essentially -a vinylidene chloride copolymer, anda-n intermediate anchoring mediumcomprising essentially a compound of the Werner type in which a trivalent nuclear atom of chromium is coordimated with a carboxylic-acido group fromthe class consisting of saturated aliphatic carboxylicv acido groups having less than six carbon atoms in the chain and bearing at least one dipole group and aromatic carboxylic acido groups bearing at least one dipole group, the dipole group moments of said dipole groups being within the range of from 0.1 to 15 Debye units, the amount of said anchoring medium being from 0.5%. to 1.0% by weight, calculated as Cr2O3, based on the dry weight of the base sheet.

4. The wrapping tissue of claim 1 wherein the hydroxylated organic polymer is regenerated cellulose. v

5. -The wrapping tissue of clairn-2 wherein the hydroxylated. organic polymer is regenerated cellulose.

6. The wrapping tissue of claim .3 wherein the hydroxylated organic polymer is regenerated cellulosa. V

7. In a process for producing moistureproof wrapping tissue having a baseof hydrophilic, hydroxylated organic polymer, the steps compris ing appling to a smooth,- dense. non-fibrous base sheet of hydrophilic, hydroxylated organic polymer a solution of a compound of the Werner type in which a trivalent nuclear atom of a metal of the group consisting of chromium, manganese, iron, cobalt and nickel is coordinated with a carboxylicacido group from the class consisting of saturated aliphatic carboxylic acido groups. having less than six carbon atoms in .thechain and bearing at least one dipole group sheetrof regenerated cellulose a solution of a' lcompoundofthe Werner .typein which .a. trivae lent nucle etom of a rnetaloi t e. roup co s st.- .in c ro um; ma ga ese, i 0 ..co a1t and nickel is coordinated with a carbcxylic acido group from the class consisting of saturated aliphatic carboxylic acido group having less than six carbon atoms in the chain and bearing at .least..onerdipole group-and aromatic carboxylic ,acido groups bearing at least one dipole group, drying the base sheet to removesolve d thereafter appling a coating of vinylidine chloride copolymer on said base sheet.

9. In a process for producing moistureproof wrapping tissue having a base of regenerated cellulose the step comprising impregnating a base sheet of regenerated cellulose gel film with an aqueous solution containing a compound of the Werner type in which a trivalent nuclear atom of a metal of the group consisting of chromium, manganese, iron, cobalt and nickel is coordinated with a carboxylic acido group from the class consisting of saturated aliphatic carboxylic acido groups having less than six carbon atoms in the chain and bearing at least one dipole group and aromatic carboxylic acido groups hearing at least one, dipole group, the amount of solution used being sufficient to apply to said base sheet from 0.2% to 1.0% by weight of said Werner type compound, calculated as the oxide of the trivalent metal, based on the dry weight of said base sheet, drying the base sheet to remove solvent, and thereafter applying a coating of vinylidene chloride copolymer on said base sheet.

10. In a process for producing moistureproof wrapping tissue having a base of hydrophilic, hydroxylated organic polymer the steps comprising applying to a smooth, dense, non-fibrous base sheet of hydrophilic hydroxylated organic polymer a solution of a compound of the Werner type in which a trivalent nuclear atom of chromium is coordinated with a carboxylic acido group from the class consisting of saturated aliphatic carboxylic acido groups having less than six carbon atoms in the chain and bearing at least one dipole group and aromatic carboxylic acido groups bearing at least one dipole group,

10 the amount of solution used being sufficient to apply to said base sheet from 0.5% to 1.0% by weight of said Werner type compound, calculated as Cr2O3, based on the weight of said base sheet,

drying the base sheet to remove solvent, and

thereafter applying a coating of vinylidene chloride copolymer on said base sheet.

11. In a process for producing moistureproof wrapping tissue having a base of regenerated cellulose the steps comprising impregnating a base sheet of regenerated cellulose gel film with an aqueous solution containing a compound of the Werner type in which a trivalent nuclear atom of chromium is coordinated with a carboxylic acido group from the class consisting of saturated aliphatic carboxylic acido groups having less than ix carbon atoms in the chain and bearing at least one dipole group and aromatic carboxylic acido groups bearing at least one dipole group, the amount of solution used being sufiicient to apply to said base sheet from 0.5% to 1.0% by weight of said Werner type compound, calculated as Crz'Os, based on the weight of said base sheet, drying the base sheet to remove solvent, and thereafter applying a coating of vinylidene chloride copolymer on said base sheet.

ARTHUR DOUGLAS McLAREN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Iler Aug. 22, 1944 

7. IN A PROCESS FOR PRODUCING MOISTUREPROOF WRAPPING TISSUE HAVING A BASE OF HYDROPHILIC, HYDROXYLATED ORGANIC POLYMER, THE STEPS COMPRISING APPLING TO A SMOOTH, DENSE, NON-FIBROUS BASE SHEET OF HYDROPHILIC, HYDROXYLATED ORGANIC POLYMER A SOLUTION OF A COMPOUND OF THE WERNER TYPE IN WHICH A TRIVALENT NUCLEAR ATOM OF A METAL OF THE GROUP CONSISTING OF CHROMIUM, MANGANESE, IRON, COBALT AND NICKEL IS COORDINATED WITH A CARBOXYLIC ACIDO GROUP FROM THE CLASS CONSISTING OF SATURATED ALIPHATIC CARBOXYLIC ACIDO GROUPS HAVING LESS THAN SIX CARBON ATOMS IN THE CHAIN AND BEARING AT LEAST ONE DIPOLE GROUP AND AROMATIC CARBOXYLIC ACIDO GROUPS BEARING AT LEAST ONE DIPOLE GROUP, THE AMOUNT OF SOLUTION USED BEING SUFFICIENT TO APPLY TO SAID BASE SHEET FROM 0.2% TO 1.0% BY WEIGHT OF SAID WERNER TYPE COMPOUND, CALCULATED AS THE OXIDE OF THE TRIVALENT METAL, BASED ON THE DRY WEIGHT OF SAID BUASE SHEET, DRYING THE BASE SHEET TO REMOVE SOLVENT, AND THEREAFTER APPLYING A COATING OF VINYLISENE CHLORIDE COPOLYMER ON SAID BASE SHEET. 